Study Notes on Hydrocarbons

Hydrocarbons

Inquiry Question

• How can hydrocarbons be classified based on their structure and reactivity?

Classification and Functional Groups

• Students will:   - Construct models, identify functional groups, and write structural and molecular formulae for homologous series of organic chemical compounds, up to C8 (ACSCH035).   - Homologous series include:     - Alkanes     - Alkenes     - Alkynes   - Conduct investigations to compare properties of organic compounds and explain differences based on bonding (ACSCH035).   - Analyze molecular shapes formed by carbon atoms in single, double, and triple bonds.   - Explain properties within and between homologous series of alkanes with reference to intermolecular and intramolecular bonding.   - Describe procedures for safe handling and disposal of organic substances (ACSCH075).   - Examine environmental, economic, and sociocultural implications of hydrocarbon extraction and usage.

Properties of Alkanes

• Alkanes are covalent molecular substances, sharing properties with other covalent molecules.   - Electronegativities:     - Carbon: 2.4     - Hydrogen: 2.1     - Both values are similar, leading to similar properties.   - Most hydrocarbon molecules are symmetrical, making them non-polar.   - Physical properties of alkenes and alkynes: Similar structure to alkanes leads to shared physical properties.

Melting and Boiling Points

• Key points:   - Relatively low melting and boiling points.   - Dispersion forces are the only intermolecular forces present.

Effects of Molecular Size

• As molecule size increases:   - More atoms -> more electrons.   - Increased strength of dispersion forces.   - Larger molecules require more energy to overcome these forces, resulting in:     - C1-C4 alkanes as gases at room temperature.     - Pentane to C16 alkanes as liquids.     - Higher alkanes (C18+) as semi-solids (waxes, tars).

Examples of Alkanes:

• Methane:   - Weak dispersion forces   - State: Gas at room temperature
• Pentane:   - Stronger dispersion forces   - State: Liquid at room temperature
• Hexadecane:   - Even stronger dispersion forces   - State: Soft solid at room temperature

Molecular Shape Influence

• Shape effects on melting and boiling points:   - Linear molecules pack closely, allowing more dispersion forces.   - Bulky molecules pack poorly, leading to fewer dispersion forces.

Data on Alkanes’ Melting and Boiling Points

Density and Solubility of Alkanes

Density

• As molar mass increases, density of alkanes increases due to tighter packing of molecules.

Solubility

• Solubility in water:   - Applies the ‘like dissolves like’ principle.   - Water is polar; alkanes are non-polar, therefore, alkanes are insoluble in water.
• Kerosene density: 0.81 g/mL; does not mix with water and floats on its surface.

Electrical Conductivity

• Electrical Conductivity of Alkanes:
    - Alkanes do not conduct electricity because they are non-polar and lack dipole or ionic charges.

Uses of Alkanes and Alkenes

• Alkanes:
    - Methane: Main component of natural gas.   - Propane: Liquid petroleum gas (LPG).   - Pentane: Industrial solvent.   - Octane: Main component of automobile fuel.   - Nonane and Decane: Additives in petrol.

• Longer Chain Molecules:   - Used as:     - Fuel oil     - Mineral oil for lubricants     - Petroleum jelly, greases, paraffin wax, and asphalt.

• Kerosene:   - Principal hydrocarbon in aviation fuel.

Chemical and Industrial Applications

• Low molecular mass alkenes serve as:   - Feedstocks for industries producing plastics, paints, detergents, and fuels.   - Ethene (ethylene):     - Most important chemical feedstock; origin for nearly all plastics.   - Applications of Ethene:     - Feedstock for:       - Polyethylene       - Vinyl chloride to PVC       - Styrene to polystyrene       - Ethanol       - Acetaldehyde   - Also used in:     - Artificial ripening of fruits.     - General anesthesia.     - Generating oxy-acetylene flame.

Alkenes: Propene (propylene)

• Second most important feedstock, used primarily for:   - Production of polypropylene.

Reactivity of Hydrocarbons

• Reactivity in Hydrocarbons:   - Presence of double bonds in alkenes and triple bonds in alkynes greatly increases their reactivity.   - Reactions include:     - Halogens (e.g., $Cl_2$).     - Hydrogen halides (e.g., $HBr$).     - Water.     - Hydrogen.
• Alkenes can participate in:   - Polymerization Reactions:     - Monomer units of ethene join to form polyethene.
• Alkanes:   - Less reactive than alkenes; participate in combustion and substitution reactions.

Environmental and Health Risks Related to Hydrocarbons

• Potential hazards from organic chemicals necessitate:   - Risk identification and precautionary measures for use and disposal.

Combustion Chemicals Release

• Alkanes as fuels emit:   - Carbon dioxide and nitrogen oxides during combustion.
• Environmental issues caused include:   - Enhanced greenhouse effect.   - Pollution from discarded polymers.   - Increased ocean acidity.

Safe Use of Organic Chemicals

• Large volumes of organic substances in manufacturing pose risks.   - Dangerous products include:     - Paints, adhesives, cleaning chemicals, printing materials.     - Chemicals like ethanal, benzene, and ethanol.
• SDS (Safety Data Sheet):   - Essential for identifying substances, hazards, and precautions.
• Proper labeling is vital for identifying compounds and ensuring safe handling.

Risks Associated with Organic Chemicals

• Physical properties lead to identifiable hazards:   - Volatility:     - Organic compounds evaporate at room temperature.   - Flammability:     - Many organic compounds are highly flammable.     - Flashpoint:       - The lowest temperature allowing ignition; below 23°C: highly flammable.

Chemical Exposure Pathways

• Entry routes into the body:   - Inhalation (most common).   - Absorption through skin.   - Ingestion (often accidental).

Effects of Exposure

• Contact effects range from skin irritation to chronic poisoning.   - Acute Symptoms:     - Headaches, dizziness, impaired coordination, possible loss of consciousness.   - Chronic Symptoms:     - Chronic fatigue, mood changes, organ damage.

Prevention and Control Methods

• Alternatives and safer chemicals being adopted.
• Isolation and use of safety equipment like gloves, goggles, lab coats.
• Fume hoods and extractor systems for ventilation.

Disposal of Organic Compounds

• Governed by legislation; collection and treatment by waste disposal companies.
• General Rule:   - No organic waste should be washed down the sink.
• Separate waste types to avoid chemical reactions affecting environment.

Environmental Implications of Hydrocarbons

• Widespread use in various sectors like transportation, manufacturing, and household goods.   - Crude Oil Formation conditions illustrated:   - Decomposition of prehistoric organisms buried over millions of years.

Crude Oil Processing

• Fractional distillation separates hydrocarbons based on boiling points.   - Gases rise, condensing at different levels of the column.

Catalytic Cracking**

• Heavy fractions broken down into lighter fractions for higher demand; use of catalysts under controlled conditions.

Environmental Damage from Hydrocarbon Mining

• Significant illustration: Exxon Valdez oil spill resulted in ecological destruction, human fatalities, and economic loss.
• Legislative Response:   - Oil Pollution Act established after the 1989 spill for future prevention and cleanup funding.

Enhanced Greenhouse Effect from Combustion

• Fuels contribute to carbon dioxide emissions and climate change.
• Examples of Affected Areas:   - Glacial retreat, rising sea levels, biosystems altered by temperature changes.

Conclusion

The large-scale use of hydrocarbons and their implications for the environment warrant significant attention and action to mitigate their impact on public health and ecosystem sustainability.